The present invention relates to an implant device, e.g., a spinal cord stimulation (SCS) system or other programmable implant device. A spinal cord stimulation system treats chronic pain by providing electrical stimulation pulses from an electrode array placed epidurally near a patient""s spinal cord. Such a spinal cord system includes several components, ranging from implantable and external components, surgical tools, and software. The present invention emphasizes the manner in which such SCS system, or any other programmable implant system, manages and changes its operational parameters.
The operation of an implanted device depends upon the storage and use of certain operational parameters. For a pulse generator system, e.g., an SCS system, these parameters might include: stimulation pulse amplitudes, pulse durations, channel frequencies, electrode configurations, ramp rates and treatment times, and the like. For a drug delivery system, such operational parameters might further include additional parameters related to the type of drug delivery, the drug medication rate of delivery, all of which may vary over the course of a day. When it is necessary to change the operation of such an implanted device, it is necessary to modify the parameters used by the device as it carries out its intended function, e.g., delivering stimulation pulses, delivering drug medication, sensing physiological activity, or the like. The present invention relates to the manner in which these operational parameters, used by the implant system as it carries out its intended function, are changed and managed. While the invention will be described in the context and background of a spinal cord stimulation system, it is to be understood that the invention has applicability, and can be used with, numerous different types of implant devices and systems, including all types of neural stimulators and sensors, deep brain stimulators, cochlear stimulators, drug delivery systems, muscle tissue stimulators, and the like.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted pulse generator, lead wires, and electrodes connected to the lead wires. The pulse generator generates electrical pulses that are delivered to the dorsal column fibers within the spinal cord through the electrodes which are implanted along the dura of the spinal cord. The attached lead wires exit the spinal cord and are tunneled around the torso of the patient to a sub-cutaneous pocket where the pulse generator is implanted.
Spinal cord and other stimulation systems are known in the art. For example, in U.S. Pat. No. 3,646,940, there is disclosed an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the ""940 patent comprise sequential, or non-overlapping, stimuli.
In U.S. Pat. No. 3,724,467, an electrode implant is disclosed for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided with a plurality of electrodes formed thereon. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means, and must be coupled to the external controller in order for neuro-stimulation to occur.
In U.S. Pat. No. 3,822,708, another type of electrical spinal cord stimulating device is shown. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds (xcexcs) in width with a repetition rate of from 5 to 200 pulses per second (pps). A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; 5,121,754; 5,417,719 and 5,501,703.
The dominant SCS products that are presently commercially available attempt to respond to three basic requirements for such systems: (1) providing multiple stimulation channels to address variable stimulation parameter requirements and multiple sites of electrical stimulation signal delivery; (2) allowing modest to high stimulation currents for those patients who need it; and (3) incorporating an internal power source with sufficient energy storage capacity to provide years of reliable service to the patient. Unfortunately, not all of these features are available in any one device. For example, one well-known device has a limited battery life at only modest current outputs, and has only a single voltage source, and hence only a single stimulation channel, which must be multiplexed in a fixed pattern to up to four electrode contacts. Another well-known device offers higher currents that can be delivered to the patient, but does not have a battery, and thus requires the patient to wear an external power source and controller. Even then, such device still has only one voltage source, and hence only a single stimulation channel, for delivery of the current stimulus to multiple electrodes through a multiplexer. Yet a third known device provides multiple channels of modest current capability, but does not have an internal power source, and thus also forces the patient to wear an external power source and controller.
All such known devices further use different approaches for modifying or changing the operational parameters that control operation of the device. Some allow only the physician or surgeon or other medical professional to make any changes in the operating parameters, thereby making it necessary for the user (the xe2x80x9cpatientxe2x80x9d who receives the benefit from the implant device) to schedule an appointment with such professional if any changes are needed. Often, the changes needed by the patient are relatively benign (insofar as the safety of the altered treatment is concerned), and could easily be made by the patient himself or herself if only the implant device provided such capability. On the other hand, the patient must not be given carte blanche to make wide spread changes in the operating parameters, else he or she could inadvertently set up a treatment regimen delivered by the implant device that could be injurious to the patient""s health or damaging to the device. Thus, what is needed is a way for the patient to readily make appropriate changes to the operating parameters of an implant device so long as such operating parameter changes maintain the device operation within safe operating limits. The operating limits should only be changeable by the physician or other medical-professional clinician.
The present invention addresses the above and other needs by providing an implant device having the ability to perform context switching. As used herein, xe2x80x9ccontext switchingxe2x80x9d means changing one set of operational parameters to another.
In accordance with one aspect of the invention, an implant device is controlled by a set of operational parameters, and the patient may advantageously swap the current set of operational parameters with another set of operational parameters.
In accordance with another aspect of the invention, the implant device further includes a time-of-day clock, and/or sensor, and automatically changes its operational parameters from one set to another set at certain times of the day, week, or month, or upon the occurrence of certain prescribed events. For example, a nighttime operational parameter set that provides a slower stimulation rate or stimulation frequency might be automatically invoked to replace a daytime operational parameter set that defines a faster stimulation rate or stimulation frequency at a prescribed hour of the day, e.g., 10:00 PM. Similarly, the daytime operational parameter set would replace the nighttime operational parameter set at another prescribed hour of the day, e.g., 6:00 AM. Alternatively, or conjunctively, if certain threshold limits are sensed by a physiological or other sensor that is included within or coupled to the implant device, then such sensing event may automatically trigger a new set of operational parameters for the implant device aimed at treating the condition sensed (the xe2x80x9ceventxe2x80x9d), by the sensor.
In accordance with yet another aspect of the invention, each set of operational parameters that may be selected by the patient, or that is automatically invoked by the device at certain times of the day or upon the occurrence of certain events, does not exceed safe operating limits of the device as prescribed by the manufacturer of the device and/or the attending physician or other competent medical personnel. (In this context, xe2x80x9csafe operating limitsxe2x80x9d refers both to safe treatment protocols for the particular patient, as well as safe operating conditions for the design of the particular implant device.)
In accordance with still an additional aspect of the invention, the patient may define a new set of operational parameters for use with the implant device so long as all parameters included within the newly defined set of operational parameters remain within prescribed limits as set by the manufacturer of the device and/or as programmed by the attending physician or other competent medical personnel.
In one embodiment of the invention, the ability to change the current operational parameter set (OPS) of the implant device is provided by including memory circuitry within the implant device wherein a plurality of OPS""s are programably stored. Upon receipt of an appropriate command, which may be manually provided by the patient through, e.g., a hand-help programmer, or automatically generated by time-of-day or sensor circuits within (or coupled to) the implant device, the current OPS is exchanged by another OPS. Each OPS stored in the implant device is limited by an external programming unit to be within safe operating limits.
In another embodiment of the invention, a plurality of OPS""s are externally stored, e.g., in a hand-held programming device, and only the currently-used OPS is stored in the implant device. Changes to the OPS are made by transmitting the replacement OPS to the implant device through a telemetry link established with the implant device from the hand-held programming device. Thus, when the patient wishes to make a change in the OPS, he or she manually activates the appropriate controls on the hand-held programmer (HHP), and such activation causes the new OPS to be telemetered to the implant device, where it replaces the current OPS. For this embodiment, when an xe2x80x9cautomaticxe2x80x9d change to the OPS is called for, e.g., when a sensor detects the occurrence of a prescribed event that signals the need to change the OPS, such change may occur at the next available time a telemetry link is established between the HHP and implant device.
It is a feature of the present invention that the implant system also allow the user, or patient, to define a new operational parameter set (OPS) which, once defined, may be selected to replace the current operational parameter set. In accordance with such feature, the patient may only be allowed to change certain ones of the individual parameters included within the OPS, and changes to those parameters are automatically limited to fall within pre-defined safe operating limits. Therefore, should the patient attempt to set an individual parameter outside of the pre-defined safe operating limits, then the parameter value is set to its limit value closest to the out-of-limit value attempted by the patient. For example, if the safe operating range for the pulse width of a stimulating pulse is between 10 xcexcs and 1 millisecond (ms), and should the patient attempt to set the pulse width to 10 ms, then the pulse width parameter in the newly defined OPS would be set to 1 ms, the maximum limit. Similarly, should the patient attempt to set the pulse width to 5 xcexcs, then the pulse width parameter in the OPS would be set to 10 xcexcs, the minimum limit. In this manner, the patient is allowed to define a new OPS for use within the implant device, but the individual parameters within such newly-defined OPS are limited to pre-defined safe values.
An advantage of the invention is that enhanced utility is provided in an implant device. More particularly, changes to the operating parameter set of the implant device may be easily made and accommodated and executed and require little, if any, intervention by the patient.
An additional advantage of the invention, in accordance with one embodiment thereof, is that the implant device allows a patient to define a new operating parameter set for use by the implant device. Advantageously, the newly-defined parameters included within the new operating parameter set are automatically restricted or limited so as to all fall within safe operating limits. In this manner, it thus becomes impossible for the patient to inadvertently, ignorantly, or mistakenly define a new operating parameter set for the implant device that might prove to be detrimental or harmful to the patient or to the device.